Pentalogy of fallot in a Crioulo foal

Background: Cardiac anomalies account for 3.5% of congenital defects in horses. Tetralogy of Fallot (TOF) is characterized by ventricular septal defect, pulmonary stenosis, dextroposition the aorta and right ventricular hypertrophy secondary. Pentalogy of Fallot (POF) is a variation and is characterized by a defect in the right atrioventricular valve or persistence of the ductus arteriosus, in addition to the other defects observed in tetralogy. Affected animals usually have stunted growth, exercise intolerance, weakness, lethargy, cyanosis, dyspnea and syncope. The aim of this study was to describe a case of POF, as diagnosed in a Crioulo foal in southern Brazil. Case: Clinical signs were observed at the fifth day of life and were characterized by cyanosis, intense tracheal stertor, tachycardia, marked heart murmur, HR 160 bpm, RR 80 breaths/min, T 39.8°C and syncope. These signs worsened with physical activity. Endoscopic evaluation of the upper airways revealed no anatomical conformation changes or tissue dysfunction. A cardiac ultrasound showed a loss of continuity of the interventricular septum, right ventricular wall thickening and a hyperechoic appearance of the area where the right atrioventricular valve (tricuspid) should be. The crises have become more severe and more frequent, the animal began to show signs of ischemia, such as loss of motor coordination and limited mobility. The foal died at 15 days old. At necropsy the liver was congested and had a nutmeg appearance, there was foam in the trachea, and the lungs were edematous. There was hydropericardium, and the heart was increased in size with a globoid shape. The heart had thickening of the walls of the right and left ventricle and pulmonary artery stenosis. There was also an oval orifice 2.5 cm in diameter in the interventricular septum connecting the ventricles (ventricular septal defect), an overriding aorta and aplasia of the tricuspid valve. Histologically the liver had centrilobular to mediozonal necrosis, and there was pulmonary edema and congestion. Discussion: The diagnosis of pentalogy of Fallot was based on the clinical signs, the ultrasound results and the macroscopic lesions observed at necropsy. Tetralogy of Fallot is one of the most common congenital cardiac malformations observed in horses, however, in a study of congenital malformations in this species, only 3.5% had cardiac malformations out of the 608 foals examined. The prevalence of heart defects in horses compared with other domestic species is relatively low (0.1% - 0.5%). In this case, the malformation was probably sporadic because the foal was the only animal to be born with this malformation on the farm. In the Crioulo breed, congenital defect reports are scarce. In a retrospective study of equine diseases in southern Brazil over a period of 35 years, malformations were not observed in 708 horses of this breed, which is the predominant breed in the region. In the present case, the fact that the mare had another three healthy foals with the same stallion reduces the possibility that this was a case of hereditary origin. It is likely that this case is of a sporadic nature with no chance of determining the cause. The differential diagnoses in animals with lethargy, cyanosis, and exercise intolerance or syncope include complicated or multiple cardiac defects. There are no previous reports of TOF and POF in the Crioulo breed in Brazil.